[bind10-dev] Blog comment from BDB developer

Shane Kerr shane at isc.org
Thu Jun 24 21:49:49 UTC 2010


On Thu, 2010-06-24 at 18:00 +0000, Francis Dupont wrote:
> > Best we contact them soon since we need additional functionality from
> > BDB's C API to walk the zone backward as well as forward once we do a find.
> => the stupid answer is to create a cursor and to use it to get
> with DB_NEXT / DB_PREV. Of course this means to set comparison
> functions before... Now I am not an expert in BDB when a whole
> group of experts propose their help (:-)!

The problem with this is that we need the DB_NEXT/DB_PREV for handling
NXDOMAIN in DNSSEC. But with the C API if you get no match you doing get
a cursor back, you get a "no data found" return.

Evan (I think) proposed a brilliant hack of:

     1. Inserting a data record if no match is found
     2. Looking up a cursor at that record
     3. Using DB_PREV to get the covering NSEC value
     4. Deleting the data record we added

Clearly this is... sub-optimal. But I'm pretty sure it would work.

A better solution would be what Michael alluded to, which is to have a
lookup which returns "I didn't find the value you wanted, but this is
the previous/next match in the data we have". We think that the Java API
provides this functionality, so there should be no fundamental changes
to BDB to support it.


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